Submerged combustion heat-generator

ABSTRACT

A submerged combustion heat-generator enabling the obtention of a high-temperature heat-carrying fluid under very good efficiency conditions, as well as practically dry and possibly &#39;&#39;&#39;&#39;neutral&#39;&#39;&#39;&#39; combustion products. The heat generator of the invention uses a burner operating on submerged combustion in a liquid bath, for instance of water, which is subjected to a pressure of several bars.

United States Patent Guillet et al. Feb. 20, 1973 [541 SUBMERGED COMBUSTION HEAT- 2,878,644 3/1959 Fenn ..126/360 A x GENERATOR 3,060,921 10/1962 Luring et al.

3,269,385 8/1966 Mitchell et al... [75] Invemms: Gum", 3,368,548 2/1968 Santoleri et a1 ..126/360 A Saint-Mande; Luc Clement Dominique Glachant, Brunoy, both of France Primary Examiner-Charles J. Myhre [73] ASS g ee G82 (18 France, Paris, France Attorney-Kenyon & Kenyon Reilly Carr & Chapin [22] Filed: Nov. 30, 1970 [21] Appl. No.: 93,766 [57] ABSTRACT Foreign Application Priority Dina A submerged combustion heat-generator enabling the Nov. 28, 1969 France ..6941279 btemi0n of a high-temperature heat-Carrying fluid under very good efficiency conditions, as well as prac- 52 US. Cl. ..126/360 A tically y and p y n ral combustion [51] Int. Cl ..F24l1 1/20 products h h gen r tor of the invention uses a [58] Field of Search .....126/360 R, 360 A; 122/31 A; burner operating on submerged combustion in a liquid 159/16 A bath, for instance of water, which is subjected to a pressure of several bars. [56] References Cited UNITED STATES PATENTS 5 Claims, 3 Drawing Figures 3,407,805 10/1968 Bougard ..l26/360 A 1 1, 17 F -F J :I g -1-- #1 j T l rr 1 l" g 18 l I I 1' a l l I w i 1 i '15 SUBMERGED COMBUSTION HEAT-GENERATOR The present invention has essentially for its object a submerged combustion heat-generator enabling the obtention of a high-temperature heat-carrying fluid under very good efficiency conditions, as well as practically dry and possibly neutra combustion products. The heat generator of the invention is of the type using at least one burner for hydrocarbons, in particular gaseous hydrocarbons, operating on submerged combustion in a liquid bath, for instance in water.

Heat generators provided with a conventional heat exchanger and used to raise the temperature of a liquid to a temperature suitable for use, do not, as a rule, enable to regeneration more than from 70 to 80 percent of the gross heat value (GHV) of the fuel used.

Some devices called submerged combustion devices, wherein the combustion takes place within the bath to be heated, enable them to readily exceed the aforementioned values owing to the improvement of the exchange conditions. The essential advantage of submerged combustion results from the exchanges which occur at the level of the bath where the combustion takes place the combustion products issuing from the bath are saturated with water at bath surface temperature. Consequently, the amount of water which the combustion products carry along depends solely upon the temperature maintained at the bath surface.

Thus, depending on the surface temperature of the bath, the combustion products are depleted of or en-' riched with water at the level of the bath, the temperature at which the exchange balance is null being the dew temperature of the combustion products.

In some cases of use, it is therefore possible to regenerate part of the latent heat of combustion water condensation and therefore to try to obtain from the combustion a heat energy equivalent to the gross heat value of the fuel. At bath surface temperatures comprised between the dew temperature and the reference temperature (C) the efficiency of the device increases between approximately 90 percent calculated on the GHV (100 percent calculated on the net heat value or NHV) and 100 percent calculated on the GHV. At bath temperatures higher than the dew temperature, the efficiency decreases rapidly.

The dew temperature of the combustion products therefore appears to be a limiting factor for the advantages offered by submerged combustion. For example, the dew temperature of the combustion products of the Lacq gas is about 60C. Under such conditions and in the given example, the normal submerged combustion of the Lacq gas is not usable and, in fact, is not used unless the bath heating temperature is maintained below 60C, this being the maximum temperature of the heat-carrying fluid used for deriving heat energy at the level of the bath. Therefore, the principle of submerged combustion has found applications which are limited to low-temperature heating such as the heating of swimming-pool water and floor heating of premises.

Now the dew temperature of the combustion products increases considerably as the pressure of the combustion products rises. For instance, the dew temperature of the combustion products of Lacq gas (60C under normal pressure) amounts to 93C under 4 bars (pressure expressed in absolute value). At this last temperature, the efiiciency of submerged combustion is always about 88 percent (calculated on the GHV), whereas between 93C and 0C the efficiency is respectively between 88 and 100 percent (calculated on the GHV).

The heat generator of the invention, operating on submerged combustion and turning to account the above-mentioned characteristics, is remarkable notably in that the heat supplied by the combustion gases to the said bath being drawn off, for use, by at least one heat exchanger which is advantageously at least partially immerged in the said bath called main bath, the fuel and the combustive substance as well as the combustion products are subjected to a pressure higher than atmospheric pressure, for instance on the order of 4 bars.

Heating by means of hot water thus becomes possible, with efliciency rates much higher than those obtained with a conventional generator the efficiency of which is about percent calculated on the GHV.

To this end it is sufficient to maintain the combustion products under pressure subsequent to the passing through the bath and to provide for combustion under a corresponding pressure. It should be specified that the energy required for overpressure of the combustive substance and the fuel amounts, for instance under a 4 bar compression, to about 5 percent calculated on the GHV of the fuel.

The amount of water required for the saturation of the combustion products, i.e., the amount of non-condensed water carried along by the fumes issuing from the generator is then determined solely by the surface temperature of the bath.

According to another advantageous feature of the invention, the fumes issuing from the main bath are conveyed into a heat condenser-regenerator subjected to a pressure approximating that of the main bath and the bath temperature of which is advantageously lower than the dew temperature of the fumes, the calories left in the said condenser being used for heating the cold heat-carrying fluid prior to its inflow into the said exchanger which is placed in the main bath.

The combustion products issuing from the plant according to the invention are saturated with water under conditions of equilibrium pressure and temperature at the level of the condenser. Owing to this fact, the efficiency of the whole assembly is determined only by the pressure of the combustion products and by the equilibrium temperature in the condenser. For example, in the case of Lacq gas combustion, if the pressure is about 4 bars at the level of the condenser and if the equilibrium temperature is 40C (approximating the temperature of the cold heat-carrying fluid penetrating into the plant), the efficiency of the device is on the order of 97 percent calculated on the GHV.

The ef'ficiency of the whole assembly does not depend upon the temperature of the bath in the main generator and the heat-carrying fluid may leave the device at a temperature higher than the dew temperature of the combustion products in the main generator, without reducing the efficiency of the whole assembly. Under such conditions, the main generator bath water will tend to become vaporized at the level of the main bath and will be collected in the condenser. According to another advantageous feature of the invention, a circulating pump will ensure the return of the said water into the main generator bath.

The invention thus enables the production of a very hot heat-carrying fluid with excellent efficiency. In addition to this advantage, another important advantage results from the fact that the fumes issuing from the plant are practically dry. Thus in the abovementioned example, if the pressure and the temperature in the condenser are, respectively, 4 bars and 40C, the Lacq gas combustion products contain only 7 percent of the water generated by the combustion, i.e., about 1 1 grams of water per cubic meter of expanded fumes as compared to the 160 grams per cubic meter of fumes emitted by a conventional boiler. Thus, the hygrometry of the combustion products approximates that of the ambient air. Under such conditions, the phenomena of water condensation in chimneys and of formation of water vapor mist in proximity to chimneys are avoided.

If in addition, according to another feature of the invention, the harmful products of combustion such as S0,, C0, are drawn off continuously from the main bath and/or the condenser, the fumes issuing from the plant are neutral, i.e., they are comprised essentially of nitrogen.

Under such conditions, the generator as a whole is equivalent to a high-efiiciency, dry and possibly neutral" fume boiler which is advantageous in mediumtemperature heating and allows for substantial differences between the input temperature and the output temperature of the heat-carrying fluid.

The invention will be better understood and other objects, characteristics and advantages thereof will appear as the following description proceeds, with reference to the appended drawings given solely by way of example and illustrating two embodiments of the invention and wherein FIG. 1 is a diagrammatical view of a plant designed according to the invention FIG. 2 shows diagrams illustrating the variation of the efficiency of Lacq gas submerged combustion under various absolute pressures and depending on the surface temperature of the bath in the last stage FIG. 3 is a diagrammatic view of a plant designed according to a modified embodiment of the invention.

According to the embodiment illustrated in FIG. 1, the combustible mixture conveyed to a burner 1 is immerged in a hot water bath 2 maintained under pressure in a container 3. The combustion products escape under the action of the pressure in the container 3 through a conduit 4 which conveys them into a condenser-regenerator 5 subjected substantially to the same pressure (except for pressure losses in the conduit 4). A valve 6 ensures the ejection, under the desired pressure, of the non-condensed products issuing from the condenser 5.

The heat-carrying fluid enters in the cold state through a conduit 7 and is heated in a first heat exchanger 8 which may be at least partially immerged and which is placed in the condenser. The heat exchanger is advantageously so arranged, as diagrammatized in the drawing, that its coldest inlet spires are the highest in the container 5, so as to reduce to a minimum the surface temperature T, of the bath 18 of condensed water. The interest of such an arrangement results from the fact that the total efficiency of the plant is determined to a great extent by the bath surface temperature, as has been explained previously.

At the outlet of the heat exchanger 8, the heat-carrying fluid is conveyed through a conduit 9 into a heat exchanger 10 immerged in the main bath 2 of hot water under pressure. The fluid issues at 11 in the hot state. The heat-carrying fluid may be, for instance, water entering at 7 in the cold state and issuing at 11 in the hot state in the form of water or vapor.

The harmful products resulting from the combustion such as S0,, C0,, and which are dissolved in the main bath 2 may be regenerated continuously in a regenerating apparatus 12 operating according to a closed loop as shown by the dashed lines at 13. The drawing off of the harmful products in liquid solution form may also be effected wholly or partially in the bath 18.

A circulating pump 14 enables conveyance of part of the condensation water formed in the condenser 5, back into the main bath 2 through a conduit 15.

At 16 and 17 are diagrammatically. shown the devices enabling maintenance of the main bath 2 and the secondary bath 18 at constant level.

The diagram is a block diagram, but the assembly will advantageously be compact for dimensional and heat-insulation considerations.

Besides, the burners and heat exchangers may simply be immerged in a pit.

in the appended diagrams illustrated in FIG. 2 it is observed, in particular, that when the surface temperature of the bath T in the condenser is 40C and the pressure maintained at that level is of the order of 4 bars (absolute pressure) the efficiency is 98 percent calculated on the GI-IV.

In the modified form of embodiment illustrated in FIG. 3, the plant is somewhat more complex than the previous one and use is made of the principle of an at least partial prior combustion in a non-submerged combustion chamber as described in the patent application Ser. No. 93,767 filed this same day in the name of the same Applicant and entitled Submerged combustion heat-generator in particular for the production of very hot water.

In this modified form of embodiment, the combustive substance and the fuel are conveyed through conduits 10', 11 into a combustion chamber 12 which is immerged in a hot water bath 13' contained in a container 14 under pressure. The chamber 12' is in the form of a vertical cylindrical boiler body closed at its top by a wall 15'. The chamber 12' is constituted internally by a heat exchanger 16' traversed by a heat-carrying fluid. The heat exchanger 16' may be constitutedby an annular sheet of water surrounding the flame or by tubes arranged in parallel relationship to the generating lines of the chamber or arranged for instance in the form of coils. The upper wall 15 and the side wall 17 of the boiler body ensure the heat insulation of the chamber 12 with respect to the bath 13. The combustion products issuing at 21 under pressure,

1 thereafter bubble in a condenser-regenerator 24' subjected substantially to the same pressure as that of the bath 13' (except for pressure losses in the conduit 21 As already mentioned, the total efficiency of the plant is determined to a great extent by the surface temperature T, of the condensed water bath 27 in the condenser 24'.

The heat-carrying fluid enters at 25' in the cold state, passes through the exchanger 26' immerged in the bath 27 enters at 18' into the main bath 13, passes through an exchanger 19' irnmerged in the latter, and then passes through the exchanger 16' mounted in the boiler body 12. The heat-carrying fluid issues at 20 in the hot state.

As in FIG. 1, a pump 28' conveys water from the condenser 27 back to the main bath 13 through the conduit 29'. Also as in FIG. 1, the harmful products are processed in a unit 22' arranged in a loop 23'.

At 30' is diagrammatically shown a calibrated valve allowing for the ejection of the dry and neutral fumes from the plant, under the pressure existing in the condenser 24' Many modifications may be made in the embodiments just described. In particular, if it is desired to obtain very hot water or vapor with a very high efficiency, it may be useful to provide for several steps of condensation and regeneration arranged in series and the bath temperatures of which are stepped. Thus, it is possible to recover, up to the lowest surface temperature of the last bath, all the calories left in the different stages of condensation and regeneration in the various baths.

Also, there may be provided in the fume escape circuit an expansion turbine the energy of which may be used for instance to effect the compression of the fuel gases and/or combustive gases up to the pressure of the main bath.

Of course, the invention is by no'means limited to the embodiments described and illustrated, which have been given by way of example only. In particular, it comprises all the means constituting technical equivalents of the means described as well as their combinations, should the latter be carried out according to the spirit of the invention.

What is claimed is 1 A plant for heating a heat-carrying fluid circulated in said plant comprising: (1) a heating chamber, (2) a first bath of water wherewith said chamber is at least partially filled, (3) a burner operating on submerged combustion in said bath of water, (4) means for supplying said burner with a combustile mixture under pressure, (5) valve means through which the products of combustion escape into the atmosphere and which maintains a pressure of at least several bars in said heating chamber, (6) a first heat exchanger immersed in said first bath of water and through which is circulated said heat-carrying fluid for draining out from said bath of water the calories generated and left by the combustion of said combustible mixture in said heating chamber, (7) a condenser, (8) a second bath of water wherewith said condenser is at least partially filled, 9) a second heat exchanger immersed in said second bath of water, (10) means for returning water from said second bath to said first bath, (1 1) an inlet in said condenser for the combustion products generated in said heating chamber, (12) conduit means connecting the exhaust of combustion producg issuing from said heating chamber to said inlet of combustion products supplied to said condenser, (13) an outlet in said condenser connected to said valve means and (14) connecting and pumping means for circulating said heatcarrying fluid successively into said second heatexchanger and into said first heat-exchanger in which said fluid is progressively heated from its supply into the plant up to its issuance from the lant.

2. A plant according to claim 1 rrther comprising: 15) a combustion chamber immersed in said first bath of water and at least partially heat-insulated from it and wherein the combustible mixture burns at least partially prior to submerged combustion, and (16) a gas/heat-carrying fluid heat exchangers placed in said combustion chamber on the path of the said heat-carrying fluid just before its issuance from the plant.

3. A plant according to claim 2, wherein the said exchangers placed in the said baths are so arranged that their coldest exchange surfaces are situated in the upper portions of the baths.

4. A plant according to claim 2, wherein the said gas/heat-carrying fluid exchanger is constituted by a boiler body.

5. A plant according to claim 2, wherein said combustion chamber immersed in said first bath of water is cylindrical, substantially vertical and its inner wall is constituted by said gas/heat-carrying fluid exchanger which is subjected to the action of the combustion products. 

1. A plant for heating a heat-carrying fluid circulated in said plant comprising: (1) a heating chamber, (2) a first bath of water wherewith said chamber is at least partially filled, (3) a burner operating on submerged combustion in said bath of water, (4) means for supplying said burner with a combustile mixture under pressure, (5) valve means through which the products of combustion escape into the atmosphere and which maintains a pressure of at least several bars in said heating chamber, (6) a first heat exchanger immersed in said first bath of water and through which is circulated said heat-carrying fluid for draining out from said bath of water the calories generated and left by the combustion of said combustible mixture in said heating chamber, (7) a condenser, (8) a second bath of water wherewith said condenser is at least partially filled, (9) a second heat exchanger immersed in said second bath of water, (10) means for returning water from said second bath to said first bath, (11) an inlet in said condenser for the combustion products generated in said heating chamber, (12) conduit means connecting the exhaust of combustion products issuing from said heating chamber to said inlet of combustion products supplied to said condenser, (13) an outlet in said condenser connected to said valve means and (14) connecting and pumping means for circulating said heat-carrying fluid successively into said second heat-exchanger and into said first heat-exchanger in which said fluid is progressively heated from its supply into the plant up to its issuance from the plant.
 1. A plant for heating a heat-carrying fluid circulated in said plant comprising: (1) a heating chamber, (2) a first bath of water wherewith said chamber is at least partially filled, (3) a burner operating on submerged combustion in said bath of water, (4) means for supplying said burner with a combustile mixture under pressure, (5) valve means through which the products of combustion escape into the atmosphere and which maintains a pressure of at least several bars in said heating chamber, (6) a first heat exchanger immersed in said first bath of water and through which is circulated said heat-carrying fluid for draining out from said bath of water the calories generated and left by the combustion of said combustible mixture in said heating chamber, (7) a condenser, (8) a second bath of water wherewith said condenser is at least partially filled, (9) a second heat exchanger immersed in said second bath of water, (10) means for returning water from said second bath to said first bath, (11) an inlet in said condenser for the combustion products generated in said heating chamber, (12) conduit means connecting the exhaust of combustion products issuing from said heating chamber to said inlet of combustion products supplied to said condenser, (13) an outlet in said condenser connected to said valve means and (14) connecting and pumping means for circulating said heat-carrying fluid successively into said second heat-exchanger and into said first heat-exchanger in which said fluid is progressively heated from its supply into the plant up to its issuance from the plant.
 2. A plant according to claim 1 further comprising: (15) a combustion chamber immersed in said first bath of water and at least partially heat-insulated from it and wherein the combustible mixture burns at least partially prior to submerged combustion, and (16) a gas/heat-carrying fluid heat exchangers placed in said combustion chamber on the path of the said heat-carrying fluid just before its issuance from the plant.
 3. A plant according to claim 2, wherein the said exchangers placed in the said baths are so arranged that their coldest exchange surfaces are situated in the upper portions of the baths.
 4. A plant according to claim 2, wherein the said gas/heat-carrying fluid exchanger is constituted by a boiler body. 